Use a scale on your tilling board.You just won't end up with a draw weight when your bows finished.
As far as form go's you won't have the same form as you do with a compound,recurve as you will with a selfbow.Yor stance closes up.
As you step down from compound to recurvw,longbow down to selfbows you will lose draw lenth with each with selfbows being the shortest.Each changing your form a little as you go down.